Method and System for Controlling Mobility in a Communication Network, Related Network and Computer Program Product Therefor

ABSTRACT

A communication network includes at least one mobile terminal and a plurality of home agents to supply communication services to the mobile terminal. In the network, an authentication, authorization and accounting (AAA) platform is configured for reallocating the supply of the communication services to the mobile terminal from a first home agent to a second home agent of the plurality.

FIELD OF THE INVENTION

The present invention refers to techniques for managing traffic in telecommunications networks.

The invention has been developed paying particular care to the possible application in mobile networks based on IP (Internet Protocol), namely, in a more accurate way, in networks where terminal mobility is managed with the Mobile IP protocol.

In any case, reference to this particular field of application must not be intended in a limiting sense for the scope of the invention.

DESCRIPTION OF THE PRIOR ART

IP mobile networks identify a scenario in which a mobile user moves inside the network and generates traffic that is routed inside the network towards the nodes (corresponding nodes) with which the user is communicating.

During his movements, the user may have to change the access network (sub-network) that allows him to use IP services. This operation must be transparent for the user so that he can go on communicating with the corresponding nodes without interruptions.

Traditional protocols on which IP networks are based, due to their nature, are not able to manage IP terminals moving inside the network. In order to fill this gap, the IETF (Internet Engineering Task Force) standardisation body has defined the Mobile IPv6 protocol, that allows IPv6 mobile terminals to change their point of attachment to the network transparently with respect to the applications.

The Mobile IPv6 protocol is specified in document rfc3775. This is the first of different references made in the present description to standards or norms of the draft- . . . or rfc . . . types: their related information are available to the public on the filing date of the present application on the IETF web site at address http://www.ietf.org or, alternatively, in the on-line data base http://www.watersprings.org.

In case the Mobile IPv6 protocol is adopted, two IP addresses are assigned to the mobile node. The first address is its Home Address (HoA): this address never changes and is used to univocally identify the identity of the node (herein below also called mobile node or terminal). The second address is the so-called Care-of Address (CoA): this address identifies the actual mobile terminal position within the visited sub-network and then changes upon every movement from one sub-network to another.

Every movement that implies a change of visited IP sub-network compels the mobile terminal to record its own Care-of Address by a server, called Home Agent (HA), that can be found in its provider's network (also called “home network”). Any other IP terminal that tries to communicate with the mobile node, contacts the mobile node itself by using the Home Address. Through the normal IP routing, the sent traffic reaches the HA, that re-addresses it towards the actual position of the mobile node, identified by the Care-of Address. In this way, all traffic aimed to the mobile node is dispatched by the Home Agent towards the current user address, namely the Care-of Address. Then, the mobile node can be constantly able to be reached whichever its point of attachment to the network is.

FIG. 1 shows a generic scenario of use of the Mobile IPv6 protocol inside the IP network that houses a mobile node.

In particular, in FIG. 1 a mobile node 10 has available a series of access points 20 that allow it to establish a connection with the network 30 of its provider and, more in detail, allow it to open a communication session, designated with 40, through a particular server called Home Agent. The communication session 40 implies, in the shown example, receiving data traffic from a corresponding node, designated with 15. The mobile node 10 motion inside the IP network is pointed out by arrow 60. The Home Agent 50 guarantees that the traffic generated by the corresponding node 15 reaches the mobile node 10 whichever the current point of attachment of the mobile node is.

Placement and load level of the Home Agent 50 greatly affect the performance experimented by the mobile terminal, since they affect both the delay with which the mobile node receives the data traffic and the length of the temporary loss of connectivity (handoff latency) that occurs after every movement from an access point to another.

It is known [ref. draft-giaretta-mip6-authorization-eap-00] that it is possible to dynamically assign to the mobile terminal, for example when turning it on, a Home Agent that is able to provide optimum performance, namely a Home Agent that has available enough processing resources and can be found as near as possible, in terms of number of IP hops, to the mobile terminal point of attachment.

However, in time, the Home Agent, initially assigned according to these criteria, may not be any more able to provide a service with adequate quality. For example, this could occur in the following situations:

-   -   following continuous movements of the mobile terminal, it is         possible that the Home Agent ends up being rather far away from         the current point of attachment of the mobile terminal itself;         this causes a great increase of the handoff latency and the         traffic transfer delay to its destination;     -   when the amount of traffic generated by the mobile terminals         that can be found in the network changes, it is possible that         the Home Agent is subjected to a congestion state, with the         consequent incapability of managing all mobile terminals         connected thereto.

In order to solve this problem, an arrangement is known that is called Inter Home Agents Protocol (HAHA) [ref. draft-wakikawa-mip6-nemo-haha-01], that allows the mobile node to change the Home Agent being used moment by moment, bearing every time upon the apparatus that is able to guarantee the best performance.

The architecture on which the Inter Home Agents Protocol solution is based, shown in FIG. 2, provides that the mobile node 10 is served, instead of by a single Home Agent 50 (as in the case shown in FIG. 1), by a group of Home Agents 70 arranged inside the operator 30 network. All Home Agents 70 belonging to the same group periodically exchange signalling messages to synchronise information about position (namely Home Address and Care-of Address) of mobile nodes that can be found inside the network.

Due to this synchronisation procedure, the Home Agents belonging to the same group are seen by the mobile node 10 as a single “virtual” Home Agent 80, which means that the mobile node 10 can be moved from one Home Agent to the other without modifying its own Home Address, namely with a minimum impact on current communications.

This approach, however, has limitations that can make its application difficult, especially in case of big-sized networks (for example big providers/operators with a meaningful number of Home Agents):

-   -   every Home Agent must be manually configured [ref.         draft-wakikawa-mip6-nemo-haha-01, page 17] with the addresses of         all other Home Agents belonging to the same group. This makes         service management and supply complicated, especially when the         number of Home Agents that can be found in the network is great;     -   in order to allow the mobile node to keep the same Home Address         independently from the Home Agent being used every moment, the         Home Agents belonging to the same group must exchange, in a         peer-to-peer mode, a high number of signalling messages, that         are necessary for synchronising the binding tables between Home         Address and Care-of Address. This limits the scalability of the         arrangement, increasing the waste of resources, such as, for         example, bandwidth resources, in network connections and the         computation load on Home Agents.

Herein below, for completeness, the background documentation, cited as reference, is included. They mostly are IETF standards and/or working documents.

-   -   Mobility support for IPv6 (rfc3775);     -   IP Mobility Support for IPv4 (rfc3344);     -   IPv6 Stateless Address Auto-configuration (rfc2462);     -   Diameter Base Protocol (rfc3588);     -   The Internet Key Exchange (rfc2409);     -   Internet Key Exchange (IKEv2) protocol         (draft-ietf-ipsec-ikev2-15)     -   Extensible Authentication Protocol (rfc3748);     -   EAP Key Management Framework (draft-ietf-eap-keying-03);     -   MIPv6 Authorisation and Configuration based on EAP         (draft-giaretta-mip6-authorization-eap-00);     -   Authentication Protocol for Mobile IPv6         (draft-ietf-mip6-auth-protocol-00)

OBJECT AND SUMMARY OF THE INVENTION

From the previous description of the current situation, it appears that there is a need for defining a technique that allows modifying in real time, and with a minimum impact on current communications, the Home Agent being used by a mobile terminal.

Object of the present invention is satisfying the above need and in particular the invention deals with the problem of providing a solution that has not the critical points of the Inter Home Agents Protocol, and can be used to enable the mobile terminal to be always served by a Home Agent that is able to provide optimum performance, without causing any disruption of user services.

According to the present invention, this object is obtained by means of a method having the characteristics included in the following claims. The present invention also deals with a corresponding system, a network comprising such system, in addition to a computer program product that can be loaded in the memory of at least one computer and comprising portions of software code to actuate the above method. As used herein, the reference to such computer program product is meant as equivalent to the reference to means readable by a processor containing instructions for controlling a computer system in order to coordinate the performance of the method according to the invention. The reference to “at least one computer” is aimed to point out the possibility that the present invention is put to practice in a distributed and/or modular way.

An embodiment of the currently preferred invention is applied to the supply of communication services to at least one mobile terminal in a communication network comprising a plurality of Home Agents, in which the at least one mobile terminal is served by a Home Agent identified within the above plurality. The services are supplied to the mobile terminal within working sessions in a situation in which:

-   -   in the communication network an Authentication, Authorisation         and Accounting (AAA) platform is provided, and     -   the Home Agent that serves the mobile terminal is identified         within the above plurality through the AAA platform in a         selective and changing way within a single working session.

The above preferred embodiment implies, among the others, the following advantages:

-   -   performance optimisation: the assignment of a Home Agent closer         to the mobile node allows optimising the performance         experimented by the user, reducing the handoff latency and the         transfer delay of traffic routed through the Home Agent;     -   load balancing: the chance of modifying the Home Agent being         used by a certain user allows intervening in real-time on the         load division among the Home Agents being present in the         network, in order to adapt it to the type and the amount of         traffic generated by the users. For example, in order to prevent         the occurrence of a congestion state, it is possible to         dynamically decrease the load level of a certain Home Agent         making one or more mobile nodes served by another Home Agent;     -   optimum use of operator network resources: the assignment of a         Home Agent closer to the mobile node allows reducing the amount         of traffic that crosses the operator network (for example the         backbone). In particular, this guarantees an optimum         exploitation of network resources, avoiding that the traffic         related to mobile nodes uselessly transits through the         geographic connections composing the operator backbone.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, as a non-limiting example, with reference to the enclosed figures of drawings, in which:

FIGS. 1 and 2 have already been previously described;

FIG. 3 shows a possible network architecture of the herein-described arrangement;

FIG. 4 shows in more detail the network architecture of the herein-described arrangement;

FIG. 5 shows a functional flow diagram representing a procedure for re-allocating the Home Agent started by mobile node and successfully ended;

FIG. 6 shows a functional flow diagram representing a procedure for re-allocating the Home Agent requested by the mobile node but refused since it was not authorised;

FIG. 7 shows a functional flow diagram representing a procedure for re-allocating the Home Agent started by the Home Agent currently-used by the mobile node and successfully ended;

FIG. 8 shows a functional flow diagram representing a procedure for re-allocating the Home Agent started by the AAA server and successfully ended;

FIG. 9 shows a functional flow diagram representing a procedure for re-allocating the Home Agent started by the AAA server but failed since it was related to a mobile node that does not support the procedure;

FIG. 10 shows the procedure closure through accounting messages;

FIG. 11 shows a possible division into zones of an operator network;

FIG. 12 shows a metrics example among the zones into which an operator network can be divided;

FIG. 13 shows a possible new format of the Binding Update message that can be used in the context of the herein-described arrangement;

FIG. 14 shows the generic format of a Mobility Option that can be used in the context of the herein-described arrangement;

FIG. 15 shows a possible format of a Home-Agent-Relocation-Data-Mobility-Option that can be used in the context of the herein-described arrangement; and

FIG. 16 shows a possible format of a Home-Agent-Relocation-Hints-Mobility-Option that can be used in the context of the herein-described arrangement.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 3 shows with direct reference to the diagrams already shown in FIGS. 1 and 2 an example of network architecture on which the herein-described arrangement is based.

The architecture in FIG. 3 provides for the use of the Authentication, Authorisation and Accounting (AAA) platform 90 of the provider with which the user subscribed the service. This in order to make such platform, already normally present in the provider 30 network, authorise, drive and monitor the whole migration process towards a new Home Agent (Designated Home Agent), by sending configuration commands and information to the Home Agents 70, present in the network, and to the mobile node 10. Communication between Authentication, Authorisation and Accounting (AAA) platform 90 and mobile node 10 is performed with the support of the Home Agent that is currently serving the mobile node (namely the Serving Home Agent) through suitable extensions in the AAA protocol, designated with 100 in FIG. 3, and in Mobile IPv6 signalling messages, designated with 102 in FIG. 3.

Each one of the Home Agents 70 present in the network thereby operates independently from the others and manages its own addressing space. Consequently, the mobile node 10 modifies its own Home Address upon every Home Agent change. Survival of application sessions is guaranteed by providing a transitional period during which the mobile node 10 can simultaneously use the old and the new Home Addresses, so that the applications started before the beginning of the reallocation procedure can end without interruptions.

Operating in this way, though increasing the complexity of the mobile node 10, that must be able to simultaneously communicate with the old (Serving) and the new (Designated) Home Agent, it is not necessary to provide any exchange of information for coordinating the Home Agents being present in the network. An increase of system scalability and a reduction of signalling overhead are thereby obtained.

The Mobile IPv6 (MIPv6) protocol is the solution, proposed within IETF (Internet Engineering Task Force), to manage the wide-range mobility of a terminal among IPv6 networks [ref. rfc3775].

The relevant protocol allows a mobile node 10 both to access a network from different positions, preserving a single identity, and to dynamically change the point of attachment keeping the existing connections active.

As already stated, the protocol manages the mobile node mobility introducing:

-   -   two different IPv6 addresses for every mobile node, namely Home         Address and Care-of Address, and     -   an agent, called Home Agent (HA).

Of the two different addresses:

-   -   i) the first one, namely the Home Address (HoA), is an address         assigned by the provider with which the user subscribed the         service; this address never changes (at least for the whole         working session length) and is used to univocally identify the         mobile node identity;     -   ii) the second, namely the Care-of Address (CoA), is an address         belonging to the visited network, dynamically obtained by the         mobile node through IPv6 auto-configuration [ref. rfc2462]. This         address locates the current mobile node position and for such         reason changes upon every movement of the mobile node itself.

The Home Agent resides in the provider network with which the user subscribed the service (the so-called “home network”) and its task is re-addressing the traffic aimed to the mobile node 10 (namely the traffic addressed to the Home Address) to the current position of the mobile node itself (namely the Care-of Address or CoA).

Though Mobile IPv6 also introduces a communication mode, called Route Optimisation, that provides for the direct communication between mobile node 10 and corresponding node 15, without the traffic passing through the Home Agent 50, the Home Agent 50 position is particularly important for the correct operation of protocol and the performances experienced by the mobile node.

In fact, the Round Trip Time (RTT) between mobile node 10 and Home Agent 50 and, therefore, their distance, greatly affect the handoff latency, namely the time interval during which, following a handoff, the mobile node is not able to receive and send packets.

Moreover, if the communication between mobile node 10 and corresponding node 15 occurs in Bi-directional Tunnelling mode (e.g. if the corresponding node 15 does not support the extensions provided by Mobile IPv6), all data traffic must pass through the Home Agent 50 and therefore this latter one's position depending on the mobile node 10 position strongly affects the transfer delay to which the data traffic is subjected.

The arrangement described here allows assigning to the mobile terminal, upon its turning on, a Home Agent that is able to provide optimum performance, namely a Home Agent that is as near as possible, in terms of number of IP hops, to the mobile terminal connection point. This can be obtained by using some of the arrangements available in literature to dynamically configure the Mobile IPv6 terminals upon their entry in the network, such as for example the arrangement disclosed in [ref. draft-giaretta-mip6-authorization-eap-00].

When, due to its continuous movements, the mobile node greatly goes away from its own Home Agent (Serving Home Agent) and experiences a decay in Mobile IPv6 protocol performances, the herein-described arrangement allows assigning the mobile node a new Home Agent (Designated Home Agent) that is able to provide better performances than the previous one (Serving Home Agent).

Everything without causing any disruption of on-going applications and within a procedure performed under the control of the provider with which the user subscribed the service (home provider), that must authorise the Home Agent change.

FIG. 4 shows the general scenario and the elements of architecture on which the proposed arrangement depends.

In particular, the following are pointed out:

-   -   an Authentication, Authorisation and Accounting server 110 of         the mobile node home provider (namely the AAA server of the         provider with which the user subscribed the service). On the         server 110, substantially corresponding to the platform pointed         out with 90 in FIG. 3, there is a module whose function is         authorising, controlling and monitoring the Home Agent         reallocation procedure, sending configuration commands and         information to the mobile node 10 and the Home Agents 70 being         present in the network;     -   a Serving Home Agent 120, namely the Home Agent that is serving         the mobile node 10. On the Home Agent 120 there is a module that         interacts with the Authentication, Authorisation and Accounting         server 110 and acts as an intermediary for communications with         the mobile node 10;     -   a Designated Home Agent 130, namely the Home Agent designated to         serve the mobile node 10. On the Home Agent 130 there resides a         module that is able to receive from the Authentication,         Authorisation and Accounting server 110 the configuration         information for the usage of the Mobile IPv6 service by the         authorised users (e.g. Home Address, cryptographic material,         granted privileges);     -   a mobile node 10, namely the mobile node on which there resides         a module that interacts with the Authentication, Authorisation         and Accounting server 110 through the Serving Home Agent 120 and         ensures the survival of application sessions during the Home         Agent reallocation procedure.

The mechanism through which the migration from Serving Home Agent 120 to Designated Home Agent 130 is managed is based on the following technical approach.

The mobile node 10 declares to support the Home Agent change without impacts on current communications (namely in a “seamless” way) in Binding Update messages that it sends to its own Home Agent, using one of the Reserved bits provided in [ref. rfc3775, page 39-41]: Home Agent 120 and server 110 are then able to recognise which mobile nodes are able to complete the procedure.

The procedure can be started either from the mobile node 10, or from the Serving Home Agent 120, or still from the AAA server 110 of the home provider.

In the first two cases, the procedure is anyway authorised by the AAA server of the home provider 110.

In particular:

-   -   i) the mobile node can request the start of a Home Agent         reallocation if it detects the existence of a Home Agent that         could guarantee better performance (e.g. discovery of a Home         Agent in its own link through the reception of a Router         Advertisement message with bit H=1 [ref. 3775, page 61-62]);     -   ii) the Serving Home Agent 120 can activate the procedure in         case of overload;     -   iii) the Authentication, Authorisation and Accounting server 110         can give rise to the Home Agent reallocation procedure in order         to provide the mobile node 10 with a Home Agent 130 that allows         better performance, usually characterised by a shorter distance         in terms of IP hops from the mobile node 10: in order to do so,         the Authentication, Authorisation and Accounting 110 server         keeps track of all Home Agents being present in the network, of         which mobile nodes each one of them is serving and of the         position of the mobile nodes themselves.

The communication of new configuration parameters to the mobile node 10 (namely the Designated Home Agent address, the new Home Address and the related Security Associations) is obtained by defining new Mobility Options [ref. rfc3775, page 46-47] inside the Binding Update (BU) and Binding Acknowledgement (BA) messages: this approach has the advantage of freeing the start of the Home Agent reallocation procedure from re-authentication events. Communication with mobile node 10 can occur completely asynchronously (namely, it can be started at any time).

The survival of application sessions is guaranteed by introducing a mechanism for managing addresses that is similar to the one provided for the “stateless auto-configuration” procedure of IPv6 networks [ref. rfc2462]: every Home Address is associated to a state that points out whether the address can be used for starting new communications or whether it can be used only for ending existing communications.

Independently from which node activates the procedure, a mechanism is provided through which the mobile node 10 communicates to the network 30 if it supports the Home Agent reallocation procedure and, in particular, the change of Home Agent without impacts on current communications. In fact, the procedure of the proposed arrangement provides that, for a certain period, the mobile node 10 simultaneously uses two Home Addresses and, then, two Home Agents (120 and 130); this, in particular, implies that the mobile node 10 starts and maintains two IPsec Security Associations with two different nodes.

It can happen, therefore, that not all mobile nodes are configured to support this new functionality. Further, a terminal (e.g. PDA) can be unable to support the procedure because it has a limited processing capability or a reduced memory space.

For this reason, every mobile node that supports the Home Agent reallocation procedure communicates this capability thereof to the network, for example setting to 1 a bit in Binding Update messages (bit R designated with 600 in FIG. 13) that it sends to its own Home Agent; in this way, the Serving Home Agent 120 is always knowing which mobile nodes are able to change Home Agent without impacts on current communications: These information, if necessary, are sent by the Serving Home Agent 120 to the Authentication, Authorisation and Accounting server 110.

As previously observed, the Home Agent reallocation procedure can be started by the mobile node.

The mobile node can request the start of the procedure when it receives a Router Advertisement (RA) message with bit H set to 1: this means, in fact, that in the link where it is, there is a Home Agent.

The Authentication, Authorisation and Accounting server can decide authorising, or not authorising, the request coming from the mobile node 10 depending on the current network status and the user service profile.

In case the request is authorised, the whole procedure is described in FIG. 5:

-   -   in a step 200 the mobile node 10 receives a Router Advertisement         with bit H set to 1 and decides to start a Home Agent         reallocation procedure;     -   in a step 202 the mobile node 10 sends a Binding Update (BU)         message to its own Serving Home Agent 120, in which it appends a         new Mobility Option, called HA-Relocation-Hints-Mobility-Option.         This option is a Home Agent reallocation request and contains:         -   a) the address of the Home Agent that sent the Router             Advertisement;         -   b) the address that the mobile node 10 configured in the             visited link and that could be the new Home Address;     -   in a step 204 the Home Agent processes the Binding Update         message as stated in [ref. rfc3775, page 88-92]; in case a         HA-Relocation-Hints-Mobility-Option is present, the Home Agent         sends to the Authentication, Authorisation and Accounting server         110 a Diameter message of Home Agent Relocation Request         comprising the following AVP (Attribute Value Pair) attributes:         -   a) User-Name-AVP containing the Network Access Identifier of             the user requesting the procedure activation. The Network             Access Identifier is the identifier used by the user during             authentication; in general it is of the user@domain type.             The Serving Home Agent 120 knows the Network Access             Identifier of the mobile node that required the start of the             Home Agent reallocation procedure, since it shares therewith             an IPsec Security Association [ref.             draft-giaretta-mip6-authorization-eap-00, page 19];         -   b) Serving-Home-Address-AVP containing the Home Address             currently assigned to the mobile node;         -   c) Designated-Home-Agent-Address-AVP and             Designated-Home-Address-AVP, respectively containing the             address of Designated Home Agent and the new Home Address             (HoA) suggested by the mobile node in the previous             HA-Relocation-Hints-Mobility-Option;     -   in a step 206 the Authentication, Authorisation and Accounting         server 110 checks whether the mobile node 10 is authorised to         carry out the Home Agent reallocation procedure; in case the         answer is affirmative, it selects a Designated Home Agent 130,         possibly the one pointed out by the mobile node 10 (the         indications provided by the mobile node in the         HA-Relocation-Hints-Mobility-Option are interpreted as a simple         suggestion, which means that the Authentication, Authorisation         and Accounting server 110 could assign to the mobile node 10 a         Designated Home Agent and a Designated Home Address different         from the required ones), and dynamically configures it in a step         208 (e.g. using the procedure defined in [ref.         draft-giaretta-mip6-authorization-eap-00]). At the end of such         communication, the Designated Home Agent 130 has allocated the         necessary resources to manage the mobile node 10;     -   when the communication between server 110 and Designated Home         Agent 130 is ended, in a step 210, the server 110 sends a         Diameter message of Home Agent Relocation Answer to the Serving         Home Agent 120 in which it inserts the following AVP attributes:         -   a) User-Name-AVP containing the Network Access Identifier of             the mobile node 10;         -   b) Designated-Home-Agent-Address-AVP containing the address             of the Designated Home Agent 130 allocated to the mobile             node 10;         -   c) Designated-Home-Address-AVP containing the new Home             Address of the mobile node 10;         -   d) Authorisation-Lifetime-AVP containing the lifetime,             possibly equal to infinite, of the previous Home Address             (Serving Home Address). This value shows the remaining time             during which the mobile node 10 can go on using the Serving             Home Agent together with the Designated Home Agent, to             guarantee the survival of application sessions that were             already active before starting the Home Agent reallocation             procedure. In other words, this lifetime shows within how             much time the Home Agent reallocation procedure must be             fully completed;     -   the Serving Home Agent 120 receives these information and in a         step 212 communicates them to the mobile node 10 including the         HA-Relocation-Data-Mobility-Option in the Binding         Acknowledgement (BA) message. Such option shows whether the         procedure was successful through the Code field and contains the         lifetime of the previous Home Address, the Designated Home Agent         address and the new Home Address;     -   the mobile node 10 receives these information and in a step 214         negotiates an IPsec Security Association with the Designated         Home Agent 130. Afterwards, the mobile node 10 can register         itself with the Designated Home Agent 130 through Binding Update         and Binding Acknowledgement messages, respectively designated by         references 216 and 218 in FIG. 5. In this transient period, the         mobile node communicates by simultaneously using Serving Home         Address and Designated Home Address.

Communications between Authentication, Authorisation and Accounting server and Designated Home Agent can be realised according to what is defined in [ref. draft-giaretta-mip6-authorization-eap-00, page 9-12].

As stated in [ref. rfc3775, page 18-19], the mobile node 10 and the Designated Home Agent 130 must share a IPsec Security Association 214 to protect the Mobile IPv6 signalling traffic.

As a preference, differently from what has been described in [ref. draft-giaretta-mip6-authorization-eap-00], the Authentication, Authorisation and Accounting server 110 does not send to the mobile node 10 a Pre-Shared Key (PSK) for the bootstrap of such IPsec Security Association through IKE (Internet Key Exchange) [ref. rfc2409].

The shared “secret” to establish the Security Association can in fact be derived from the authentication procedure, and, in particular, from the cryptographic material exported from by the employed EAP (Extensible Authentication Protocol) method. This supposing that the mobile node uses the EAP protocol [ref. rfc3748] for accessing the network and that the Authentication, Authorisation and Accounting server can safely communicate the PSK to the Designated Home Agent: an example on how such communication can happen is described in [ref. draft-giaretta-mip6-authorization-eap-00, page 11-12].

In case the Home Agent reallocation request coming from the mobile node 10 is not authorised, the whole procedure is described in FIG. 6:

-   -   in a step 220 the mobile node 10 receives a Router Advertisement         with bit H set to 1 and decides to start a Home Agent         reallocation procedure;     -   in a step 222 the mobile node 10 sends a Binding Update (BU)         message to its own Serving Home Agent 120, in which it appends a         new mobility option, called HA-Relocation-Hints-Mobility-Option;     -   in a step 224 the Home Agent 120 processes the Binding Update         message as stated in [ref. rfc3775, page 88-92];     -   in a step 226 the Authentication, Authorisation and Accounting         server 110 decides not to authorise the request;     -   in a step 228 the Authentication, Authorisation and Accounting         server 110 replies to the Diameter message of Home Agent         Relocation Request coming from the Serving Home Agent 120 by         sending a Home Agent Relocation Answer message with a         Result-Code-AVP equal to DIAMETER AUTHORISATION REJECTED [ref.         rfc3588];     -   in a step 230 in turn the Serving Home Agent 120 communicates to         the mobile node 10 the failure of the procedure through a         HA-Relocation-Data-Mobility-Option containing the FAILURE value         in the Code field.

The Home Agent reallocation procedure can be requested and started also by the Serving Home Agent; in particular, the Serving Home Agent can request the start of the procedure for a mobile node in case it begins being overloaded and has, consequently, difficulties in managing all mobile nodes registered with it.

FIG. 7 shows the procedure flow in case the request coming from the Serving Home Agent has been regularly authorised by the Authentication, Authorisation and Accounting server. The steps composing the procedure are as follows:

-   -   the Serving Home Agent 120 in a step 240 experiments a trigger         that starts the procedure: as said, the most meaningful case is         the one with Home Agent overload;     -   the Serving Home Agent 120 activates, in a step 242, the Home         Agent reallocation procedure by sending to the Authentication,         Authorisation and Accounting server 110 a Diameter message of HA         Relocation Request, containing the Network Access Identifier of         the mobile node that it would like to stop servicing and the         corresponding Home Address. The mobile node is selected among         those supporting the Home Agent reallocation procedure, namely         among those that has sent a Binding Update with bit R equal to         1;     -   the Authentication, Authorisation and Accounting server 110         checks, in a step 244, that the Serving Home Agent is authorised         to start the Home Agent reallocation procedure for the selected         mobile node. If the answer is affirmative, the server 110         chooses, through a suitable algorithm, a Designated Home Agent         130 for that mobile node;     -   in a step 246 the server 110 negotiates with the Designated Home         Agent 130 the Mobile IPv6 service and the corresponding         resources to be allocated. This can be realised by using, for         example, the procedure described in         [draft-giaretta-mip6-authorization-eap-00];     -   in a step 248, once having completed the resource allocation         procedure on the Designated Home Agent 130, the server 110 sends         to the Serving Home Agent 120 a HA Relocation Answer message in         which it inserts the following AVP attributes:         -   a) User-Name-AVP containing the Network Access Identifier of             the mobile node 10;         -   b) Designated-Home-Agent-Address-AVP with the Designated             Home Agent address;         -   c) Designated-Home-Address-AVP with the new Home Address;         -   d) Authorisation-Lifetime-AVP containing the lifetime of the             previous Home Address;     -   as soon as the Serving Home Agent 120 receives, in a step 250, a         Binding Update message from the user (in order to speed up the         procedure, the Serving Home Agent can send a Binding Refresh         Request, BRR, message requesting the mobile node 10 to         immediately send a new Binding Update), it replies, in a step         252, with a Binding Acknowledgement message containing a         HA-Relocation-Data-Mobility-Option. Such option contains the         lifetime of the previous Home Address, the Designated Home         Address and the new Home Address (namely the configuration data         provided by the server 110 in the previous Diameter message of         HA Relocation Answer). Also in this case, the PSK for         bootstrapping the IPsec Security Association between mobile node         and Home Agent is derived from EAP;     -   at that time, in a step 254, the mobile node 10 starts an IPsec         Security Association with the Designated Home Agent and performs         the Mobile IPv6 registration with it (namely the transmission of         Binding Update and Binding Acknowledgement messages,         respectively designated by references 256 and 258 in FIG. 7).

Also in this case, the Authentication, Authorisation and Accounting server 110 can decide not to authorise the Home Agent reallocation procedure requested by the Serving Home Agent; this is performed by sending to the Serving Home Agent a Diameter message of Home Agent Relocation Answer with Result-Code-AVP equal to DIAMETER_AUTHORIZATION_REJECTED.

FIG. 8 shows the Home Agent reallocation procedure in case it is started by the Authentication, Authorisation and Accounting server 110.

At least depending on experiences so far performed by the Applicant, this case is probably the most meaningful among the disclosed ones.

The Authentication, Authorisation and Accounting server 110 detects, normally during a re-authentication procedure, that the mobile node is far away in terms of IP hops from the Serving Home Agent and therefore would benefit from the assignment of a new Home Agent. Information about the mobile node position can be easily obtained starting from the IP address of the Network Access Server from which the user performed the re-authentication procedure.

The procedure comprises the following steps:

-   -   in a step 260 the server 110 selects a suitable Designated Home         Agent, 130, and allocates the resources by following, for         example, the approach described in [ref.         draft-giaretta-mip6-authorization-eap-00];     -   once the server 110 in a step 262 has configured the Designated         Home Agent 130, it sends in a step 264 a Diameter message of HA         Relocation Activation Request to the Serving Home Agent 120         inserting the following AVP attributes:         -   a) User-Name-AVP containing the user's Network Access             Identifier;         -   b) Serving-Home-Address-AVP containing the Home Address             currently assigned to the mobile node;         -   c) Designated-Home-Agent-Address-AVP containing the             Designated Home Agent address;         -   d) Designated-Home-Address-AVP containing the new Home             Address assigned to the mobile node 10;         -   e) Authorisation-Lifetime-AVP containing the lifetime,             possibly equal to infinite, of the previous Home Address             (Serving Home Address);     -   in a step 266 the Serving Home Agent 120 immediately sends a         Binding Refresh Request (BRR) message to the mobile node 10 in         order to solicit the transmission of a Binding Update. The         transmission of the BRR allows avoiding Diameter communication         time-out problems between Serving Home Agent 120 and server 110,         since, otherwise, it is not possible to deterministically         provide when the next Binding Update will be received from the         mobile node 10;     -   after having received, in a step 268, the Binding Update from         the mobile node 10 that must carry out the Home Agent         reallocation procedure, in the following Binding         Acknowledgement, step 270, the Serving Home Agent 120 inserts a         HA-Relocation-Data-Mobility-Option containing the lifetime of         the previous Home Address, the Designated Home Agent address and         the new Home Address;     -   in a step 272 the Serving Home Agent 120 replies to the server         110 with a Home Agent Relocation Activation Answer message, in         which it points out that the mobile node 10 has received         information for completing the procedure;     -   afterwards, the mobile node 10 can negotiate the IPsec Security         Association with the Designated Home Agent 130, step 274, and         perform the Mobile IPv6 registration with it, steps 276 and 278.

As pointed out previously, the mobile node communicates to the Serving Home Agent, by means of Binding Update messages, whether it supports the Home Agent reallocation procedure and the Mobility Options defined here. These information reach the Serving Home Agent and not the Authentication, Authorisation and Accounting server: for such reason, the Authentication, Authorisation and Accounting server can start a Home Agent reallocation procedure for a mobile node that in practice does not support such functionality.

In such case, in a step 280 in FIG. 9, the Serving Home Agent 120 becomes aware that the mobile node 10 does not support the requested functionality. In a step 282 the Serving Home Agent 120 communicates to the server 110 that the procedure cannot be carried out through a HA Relocation Activation Answer message with Result-Code-AVP equal to DIAMETER_UNABLE_TO_COMPLY.

Based on the previously defined procedure, following the exchange with the Serving Home Agent of the Binding Update and Binding Acknowledgement messages containing the new Mobility Option and the consequent registration with the Designated Home Agent, the mobile node has two Home Addresses associated with one or more Home Agents.

The way in which the mobile node manages the simultaneous presence of these two registrations and the criteria based on which it completely deletes the registration from the Serving Home Agent will now be described.

In this context, it is desirable that the Home Agent reallocation procedure has no influence on on-going communications.

For example, if the mobile node, as soon as the registration with the Designated Home Agent is ended, carried out the deletion of the registration with the Serving Home Agent, possible on-going sessions would not remain active, since identified by the Home Address related to the Serving Home Agent (namely the Serving Home Address).

The approach proposed in the herein-described arrangement is similar to the one used in IPv6 networks for stateless host configuration [ref. 2462].

The herein-described arrangement inserts a state machine that regulates the use of a Home Address and, in particular, points out whether the Home Address can be used only for already active communications or also for starting new communications.

The states that can be assumed by a Home Address are:

-   -   a first state, here called Preferred Home Address: it is an         address for which there is no restriction of use for upper         levels. This implies that such address can be used for starting         new communications; in the herein-described procedure, a Home         Address is in the Preferred state since when it is assigned to         the mobile node till when the Home Agent reallocation procedure         is completed by assigning a new Home Address (Designated Home         Address);     -   a second state, here called Deprecated Home Address: it is an         address whose use is allowed only for already activated         communications; therefore, it cannot be used for starting new         communications. The Home Address goes from Preferred state to         Deprecated state when the Home Agent reallocation procedure is         completed and the mobile node has registered itself with the         Designated Home Agent; and     -   a third state, here called Invalid Home Address: an address in         this state cannot be used by the mobile node neither for new         communications nor for existing communications. The Home Address         goes from Deprecated state to Invalid state when the mobile node         has ended all communications previously activated with that         address; to avoid that a Home Address remains in the Deprecated         state fro too much time (for example in case of communications         with a very long duration), an address can pass to the Invalid         state also following the elapse of a time-out (namely the         lifetime pointed out by the Authentication, Authorisation and         Accounting server in the Authorisation-Lifetime-AVP). It must be         noted that, at the expiration of such time-out, that anyway         should be characterised by a rather high value, possible         communications linked to such address are stopped.

In order to ensure the correct operation of the procedure, it is important that the Authentication, Authorisation and Accounting server 110 gets to know when the procedure itself is completed: in particular, it is necessary to provide that the Authentication, Authorisation and Accounting server 110 is informed about when the mobile node is registered with the Designated Home Agent and when it deletes its registration with the Serving Home Agent. These information are made available to the Authentication, Authorisation and Accounting server 110 for two reasons:

-   -   they are used as confirmation of the correct operation of the         procedure, in such a way that the Authentication, Authorisation         and Accounting server 110 always knows the Home Agent that is         serving a particular mobile node;     -   they can be used by the Authentication, Authorisation and         Accounting server 110 to decide whether to authorise a new Home         Agent reallocation procedure; for example, the Authentication,         Authorisation and Accounting server 110 can decide not to         authorise a mobile node or Serving Home Agent request in case         the mobile node itself has not yet completed a previous Home         Agent reallocation.

The proposed arrangement provides that these information are supplied to the Authentication, Authorisation and Accounting server 110 using the accounting Diameter messages; the procedure consists in the steps used in FIG. 10:

-   -   in a step 300 the mobile node 10 sends a Binding Update message         to the Designated Home Agent 130;     -   in a step 302 the Designated Home Agent 130 replies to the         mobile node 10 with a Binding Acknowledgement;     -   after the mobile node 10 has registered with the Designated Home         Agent 130, in a step 304 the Designated Home Agent 130 itself         sends to the server 110 an Accounting Start message to confirm         the occurred registration; from this message, the server 110         comprises that the mobile node 10 has begun the actual Home         Agent reallocation procedure and that the mobile node itself is         registered with two different Home Agents (namely the Serving         Home Agent and the Designated Home Agent);     -   in the period designated with 306, it happens that the mobile         node 10 simultaneously uses Serving Home Agent 120 and         Designated Home Agent 130;     -   in a step 308, the mobile node 10 sends to the Serving Home         Agent 120 a Binding Update message with

Lifetime equal to zero, in order to explicitly delete its own registration, and in a step 310 it receives the corresponding Binding Acknowledgement message. Alternatively, the mobile node 10 can let its own registration with the Serving Home Agent 120 spontaneously elapse, ceasing to periodically confirm its validity by sending Binding Update messages to the Serving Home Agent 120;

-   -   after having removed the state related to the mobile node 10, in         a step 312, the Serving Home Agent 120 sends to the         Authentication, Authorisation and Accounting server 110 a         Diameter message of Accounting Stop, as it occurs for any         Network Access Server. The server 110 understands from this         message that the mobile node is not registered any more on the         Serving Home Agent 120 and that, therefore, the Home Agent         reallocation procedure is wholly ended.

As stated in [ref. rfc3775, page 18-19] it is necessary that mobile node and Home Agent establish an IPsec Security Association, for example by using Internet Key Exchange [ref. rfc2409], before exchanging any Binding Update or Binding Acknowledgement messages.

Differently from what is described in [ref. draft-giaretta-mip6-authorization-eap00], in the herein-proposed arrangement it is provided that the Pre-Shared Key necessary for bootstrapping the Internet Key Exchange is not explicitly sent to the mobile node, but is derived from the mobile node itself based on the EAP key hierarchy.

The procedure to derive and use such key is described herein below.

At the end of the EAP communication, the mobile node and the Authentication, Authorisation and Accounting server 110 share two keys derived from the particular authentication method being used: they are the Master Session Key (MSK) and the Extended Master Session Key (EMSK) [ref. draft-ietf-eap-keying-03, page 13-17]. This latter key can in turn be used to derive other keys, defined as Application Master Session Key (AMSK), that are directly used by the applications [ref. draft-ietf-eap-keying-03, page 13-17]; in particular, it is possible to derive an Application Master Session Key specific for Mobile IPv6 that can be used as PSK in IKE phase 1.

Such key is derived from the EMSK both by the mobile node 10 and by the Authentication, Authorisation and Accounting server 110; this latter one must afterwards communicate it to the Home Agent. Such communication can be performed through the Diameter protocol, for example with the approach defined in [ref. draft-giaretta-mip6-authorization-eap-00].

A possible function for deriving from the EMSK a AMSK for Mobile IPv6 is the following:

-   -   KDF (K,L,D,O)=T1|T2|T3|T4| . . .         -   T1=prf (K, S|0x01)         -   T2=prf (K, T1|S|0x02)         -   T3=prf (K, T2|S|0x03)

where

-   -   prf=HMAC-SHA1     -   K=EMSK     -   L=key label=“MIPv6 Key”     -   D=application data=Home Agent Address     -   O=OutputLength (2 bytes)     -   S=L “\0”|D|O

Herein below a procedure is described that can be used by the Authentication, Authorisation and Accounting server 110 to choose the Designated Home Agent 130 to be assigned to the mobile node during the Home Agent reallocation procedure.

The approach is based on the division of the operator's access network into different zones, each one characterized by the presence of one or more Home Agents as shown in FIG. 11.

The mobile node 10 that can be found in the zone 400 is normally managed by the Home Agent 410 corresponding to such zone; following a movement that implies a zone change, 420 or 440, the network must decide whether the affected zones are enough far away to justify the start of a Home Agent reallocation procedure.

In addition to the zones into which the access network is divided, it can be useful to define one or more roaming zones 460 comprising the Home Agents 470 dedicated to managing the users that are roaming in the networks of other providers 480. FIG. 11 shows such Home Agents 470 as placed inside the backbone network 490 next to the interconnection points with other networks.

To manage the Home Agent reallocation procedures through this approach, the server 110, possibly referring to a centralised data-base 500 (e.g. a LDAP data-base), preferably keeps the following data structures:

-   -   Zone Table: in this table, the Authentication, Authorisation and         Accounting server 110 keeps the list of zones into which the         access network has been divided and the possible roaming zones;     -   Network Access Server Table: in this table, the Authentication,         Authorisation and Accounting server 110 keeps the identifier of         every Network Access Server 510 being present in the network         (e.g. router, Access Point) and a list of information linked         thereto, among which in particular the IP address and the zone         to which it belongs;     -   Home Agent Table: for every Home Agent, an identifier is kept         (e.g. IP address, Network Access Identifier) together with other         information both on node characteristics (type, maximum         capacity, etc.) and on current node load level (namely number of         served users, that can be updated depending on Accounting         information). Moreover, in this table the Authentication,         Authorisation and Accounting server 110 keeps information about         the zone served by every Home Agent.

From information contained in these data structures, the Authentication, Authorisation and Accounting server 110 is able to timely know in which zone a particular mobile node can be found, the zone to which its Serving Home Agent belongs and the global network situation. These information however can be not enough to decide when it is convenient, or even necessary, to perform the Home Agent reallocation procedure; for such purpose, a metrics is determined that allows providing an indication of the distance between zones and depending on such metrics deciding whether to start the procedure.

An example of static metrics for the network in FIG. 11 and its use for the purpose of taking a final decision about executing the procedure is shown in FIG. 12. The table rows represent possible zones (400, 420, 440, 460) pertaining to the Serving Home Agent, while the columns similarly represent the zones in which the mobile node can be found during its movements. Each box contains a value representing the distance that separates the row-associated zone from the column-associated zone. By referring to this table, the Authentication, Authorisation and Accounting server 110 can obtain at any time the metrics associated with the distance from the zone pertaining to the Serving Home Agent to the zone in which the mobile node can be found. Depending on the value of such metrics, the server 110 can decide whether to start or not the Home Agent reallocation procedure. As an example, it is possible to assume a metrics on three levels (1, 2 and 3) having the following meaning:

-   -   1=the Home Agent reallocation procedure is not required (namely         the zone pertaining to the Serving Home Agent coincides with the         zone in which the mobile node can be found, or anyway the two         zones are very near in terms of number of IP hops);     -   2=the Home Agent reallocation procedure is optional (namely the         zone pertaining to the Serving Home Agent does not coincide with         the zone in which the mobile node can be found, but anyway the         two zones are not spaced apart enough to make it strictly         necessary to use the Home Agent reallocation procedure);     -   3=the Home Agent reallocation procedure is compulsory (namely         the zone pertaining to Serving Home Agent is so far away from         the zone in which the mobile node can be found that the recourse         to the Home Agent reallocation procedure is strongly advised).

An alternative arrangement provides for dynamically updating the metrics depending on the instantaneous network load, that can be evaluated through the Round Trip Time (RTT) estimate among different Home Agents and RTT among the mobile nodes being present in every zone and the corresponding Serving Home Agents.

Herein below the format of previously-defined Mobility Options and AVP (Attribute Value Pair) attributes is included.

FIG. 13 shows the Binding Update message format, in which bit 600 is pointed out, defined by the herein-described arrangement: bit 600 (R) is set to 1 by the mobile node if it supports the Home Agent reallocation procedure.

FIG. 14 shows the format of a generic Mobility Option, as specified in [ref. rfc3775, page 46-47]; as can be noted, it is a format of the TLV (Type, Length, Value) type with the presence of Type 610, Length 620 and Data 630 fields.

FIG. 15 shows the Home-Agent-Relocation-Data-Mobility-Option. The defined fields are as follows:

-   -   field 640 (Code): it shows the procedure result. This field can         assume the following values:         -   i) 0=Success         -   ii) 128=Failure     -   field 642 (Reserved): field reserved for future uses;     -   field 644 (Lifetime): this field points out the value in units         of four seconds of the lifetime of the Home Address currently         allocated to the mobile node (the Home Address related to the         Serving Home Agent, namely the Serving Home Address). This value         can also be infinite;     -   field 646 (Home Address): it contains the new Home Address         allocated to the user (namely the Designated Home Address);     -   field 648 (Home Agent Address): it contains the Designated Home         Agent address.

FIG. 16 shows the format of the Home-Agent-Relocation-Hints-Mobility-Option. It can be noted that it shows the Home Address 646 and Home Agent Address 648 fields already introduced for the Home-Agent-Relocation-Data-Mobility-Option. These fields can contain a null value in case the mobile node requests a Home Agent reallocation procedure without having received any Router Advertisement with bit H=1.

The Diameter messages used in the arrangement proposed here are as follows:

-   -   Home Agent Relocation Request. This message is sent by the         Serving Home Agent to the Authentication, Authorisation and         Accounting server for requesting the start of the Home Agent         reallocation procedure; it contains the following AVP         attributes:         -   User-Name-AVP;         -   Serving-Home-Address-AVP;         -   Designated-Home-Address-AVP (optional);         -   Designated-Home-Agent-Address-AVP (optional).     -   Home Agent Relocation Answer. This message is sent by the         Authentication, Authorisation and Accounting server to the         Serving Home Agent to communicate new configuration parameters         that have to be delivered to the mobile node as part of the Home         Agent reallocation procedure; it contains the following AVP         attributes:         -   User-Name-AVP;         -   Designated-Home-Address-AVP;         -   Designated-Home-Agent-Address-AVP;         -   Authorisation-Lifetime-AVP.     -   Home Agent Relocation Activation Request. This message is sent         by the Authentication, Authorisation and Accounting server in         case it proposes to the Serving Home Agent a Home Agent         reallocation procedure for a particular mobile node; it contains         the following AVP attributes:         -   User-Name-AVP;         -   Serving-Home-Address-AVP;         -   Designated-Home-Address-AVP;         -   Designated-Home-Agent-Address-AVP;         -   Authorisation-Lifetime-AVP.     -   Home Agent Relocation Activation Answer. This message is sent by         the Serving Home Agent to communicate to the Authentication,         Authorisation and Accounting server that the mobile node has         been warned about the need of performing the Home Agent         reallocation procedure; it contains the following AVP         attributes:         -   User-Name-AVP;         -   Result-AVP.

The AVP attributes used and/or defined in this document are the following (the description is based on conventions and data types specified in [ref. rfc3588]):

-   -   User-Name-AVP (AVP Code 1). This AVP contains the user's         user-name expressed in the form of a Network Access Identifier.         The AVP is of the UTFSString type.     -   Serving-Home-Address-AVP. The AVP Data field of this AVP is of         the IPAddress type and contains the Home Address related to the         Serving Home Agent.     -   Designated-Home-Address-AVP. The AVP Data field of this AVP is         of the IPAddress type and contains the Home Address related to         the Designated Home Agent.     -   Designated-Home-Agent-Address-AVP. The AVP Data field of this         AVP is of the IPAddress type and contains the Designated Home         Agent address.     -   Authorisation-Lifetime-AVP (AVP Code 291). This AVP is of the         Unsigned32 type; the value contained in the AVP Data field         represents the lifetime in seconds of the authorisation to use         the services for a certain user. In case of the Home Agent         reallocation procedure, this value points out the remaining time         during which the mobile node can go on using the Serving Home         Agent together with the Designated Home Agent, to guarantee the         survival of application sessions that were already active before         the start of the Home Agent reallocation procedure.

The described Home Agent reallocation procedure has been detailed taking into account a particular scenario characterised in this way:

-   -   the mobile node authentication to authorise network access is         realised through an EAP method (e.g. EAP-SIM, EAP-AKA) that is         able to export keys that can be used by other applications;     -   the mobile node movements between different IP sub-networks are         managed through the Mobile IPv6 protocol, that guarantees the         survival of application sessions across mobility events;     -   the signalling messages exchanged between mobile node and Home         Agent are protected (namely authentication, integrity and         confidentiality) through an IPsec Security Association;     -   the IPsec Security Association between mobile node and Home         Agent is dynamically established through the IKE protocol;     -   the communication between the Authentication, Authorisation and         Accounting server and the Home Agents being present in the         network (namely Serving Home Agent and Designated Home Agent) is         realised through the Diameter protocol.

The procedure of the described arrangement, however, can be extended, for example and without limitation, to situations in which:

-   -   the mobile node authentication is realised through methods other         than EAP, but anyway able to generate (on the mobile node and on         the Authentication, Authorisation and Accounting server)         cryptographic material that can be used by other applications         (e.g. Mobile IP);     -   the mobile node movements are managed by using the Mobile IPv4         protocol [ref. rfc3344], or other mobility management protocols         based on similar architectural principles;     -   signalling messages exchanged between mobile node and Home Agent         are protected through a mechanism that is different from IPsec         (e.g. the arrangement described in [ref.         draft-ietf-mip6-auth-protocol-00]), but anyway based on the         existence of a shared secret (e.g. Pre-Shared Key) between         mobile node and home agent     -   the IPsec Security Association between mobile node and Home         Agent (Serving or Designated one) is dynamically established         through the IKEv2 protocol [ref. draft-ietf-ipsec-ikev2-15], or         other mechanisms that allow performing the bootstrap of an IPsec         Security Association starting from a shared secret (e.g.         Pre-Shared Key);     -   the communication between Authentication, Authorisation and         Accounting server and Home Agent (Serving Home Agent and         Designated Home Agent) is realised using any other protocol that         is able to manage the transport of generic information contents         (RADIUS, SNMP, etc.).

Consequently, without departing from the inventive principle, the constructive parts and the embodiments can change, even greatly, with respect to what is described and shown, merely as a non-limiting example of possible embodiments of the invention, without thereby departing from the scope of the invention, as defined by the claims that follow. 

1-38. (canceled)
 39. A method for reallocating, in a communication network comprising a plurality of Home Agents, a supply of communication services to at least one mobile terminal from a first Home Agent identified within said plurality to another Home Agent, wherein said at least one mobile terminal uses at least one address to be served by the first Home Agent, the method comprising the steps of: providing, in said communication network, an Authentication, Authorisation and Accounting (AAA) platform; selecting through said AAA platform, while said at least one mobile terminal is served by said first Home Agent, a second Home Agent for serving said at least one mobile terminal; and reallocating the supply of said communication services to said at least one mobile terminal from said first Home Agent to said second Home Agent, comprising sending from said AAA platform to said at least one mobile terminal through said first Home Agent configuration information for configuring said at least one mobile terminal for accessing said communication services through said second Home Agent.
 40. The method according to claim 39, further comprising sending from said AAA platform to said second Home Agent configuration information for configuring said second Home Agent for allowing the supply of said communication services to said at least one mobile terminal.
 41. The method according to claim 39, further comprising reallocating the supply of said communication services to said at least one mobile terminal from the first Home Agent to the second Home Agent of said plurality, the reallocation being started by said AAA platform.
 42. The method according to claim 39, further comprising reallocating the supply of said communication services to said at least one mobile terminal from the first Home Agent to the second Home Agent of said plurality, when at least one of the following conditions occurs: said at least one mobile terminal detects that said second Home Agent is configured to provide said communication services with better performance with respect to said first Home Agent, and said first Home Agent detects an occurrence of an overload situation.
 43. The method according to claim 39, further comprising reallocating the supply of said communication services to said at least one mobile terminal from the first Home Agent to the second Home Agent of said plurality, when said AAA platform detects that said second Home Agent is configured to provide to said at least one mobile terminal said communication services with better performance with respect to said first Home Agent.
 44. The method according to claim 40, wherein said configuration information sent to said second Home Agent comprises at least one of the following parameters: an identifier of said at least one mobile terminal, a new address assigned to said at least one mobile terminal for communications with said second Home Agent, and parameters for activating a security association that can be used in communications between said at least one mobile terminal and said second Home Agent.
 45. The method according to claim 39, wherein said configuration information sent to said at least one mobile terminal through said first Home Agent comprises at least one of the following parameters: an address of said second Home Agent, a new address assigned to said at least one mobile terminal for communications with said second Home Agent, and a lifetime, said lifetime being of any duration including an infinite duration, of the address used by said at least one mobile terminal for communications with said first Home Agent.
 46. The method according to claim 40, further comprising establishing a security association for protecting communications between said at least one mobile terminal and said second Home Agent by: sending, from said AAA platform to said second Home Agent, at least one secret to establish said security association, and deducing said at least one secret from said at least one mobile terminal from an authentication procedure performed with said AAA platform.
 47. The method according to claim 39, further comprising configuring said communication network as a network where terminal mobility is managed with the Mobile Internet Protocol.
 48. A mobile terminal accessing communication services in a communication network, comprising a plurality of Home Agents and an Authentication, Authorisation and Accounting (AAA) platform, wherein said mobile terminal uses at least one address to be served by a Home Agent identified within said plurality and wherein said AAA platform is configured for selecting, while said at least one mobile terminal is served by a first Home Agent in said plurality, a second Home Agent configured to serve said at least one mobile terminal, wherein said mobile terminal receives from said AAA platform, through said first Home Agent, configuration information for configuring the access to said communication services through said second Home Agent, thereby reallocating the supply of said communication services from said first Home Agent to said second Home Agent.
 49. The mobile terminal according to claim 48, wherein said configuration information sent to said at least one mobile terminal through said first Home Agent comprises at least one of the following parameters: an address of said second Home Agent, a new address assigned to said at least one mobile terminal for communications with said second Home Agent, and a lifetime, said lifetime being of any duration including an infinite duration, of the address used by said at least one mobile terminal for communications with said first Home Agent.
 50. An Authentication, Authorisation and Accounting (AAA) platform in a communication network comprising at least one mobile terminal and a plurality of Home Agents, for providing communication services to said at least one mobile terminal, wherein said at least one mobile terminal uses at least one address to be served by a Home Agent identified within said plurality, said AAA platform being configured to: select, while said at least one mobile terminal is served by a first Home Agent in said plurality, a second Home Agent configured to serve said at least one mobile terminal, and reallocate the supply of said communication services to said at least one mobile terminal from said first Home Agent to said second Home Agent by sending to said at least one mobile terminal through said first Home Agent configuration information for configuring said at least one mobile terminal for accessing said communication services through said second Home Agent.
 51. The AAA platform according to claim 50, further configured to send to said second Home Agent configuration information for configuring said second Home Agent to allow the supply of said communication services to said at least one mobile terminal.
 52. The AAA platform according to claim 50, further configured to start reallocating the supply of said communication services to said at least one mobile terminal from said first to second Home Agents.
 53. The AAA platform according to claim 50, wherein the supply of said communication services to said at least one mobile terminal is reallocated from said first to second Home Agents when said AAA platform detects that said second Home Agent is configured to provide to said at least one mobile terminal said communication services with better performance with respect to said first Home Agent.
 54. The AAA platform according to claim 51, wherein said configuration information sent to said second Home Agent comprises at least one of the following parameters: an identifier of said at least one mobile terminal, a new address assigned to said at least one mobile terminal for communications with said second Home Agent, and parameters for activating a security association that can be used in communications between said at least one mobile terminal and said second Home Agent.
 55. The AAA platform according to claim 50, wherein said configuration information sent to said at least one mobile terminal through said first Home Agent comprises at least one of the following parameters: an address of said second Home Agent, a new address assigned to said at least one mobile terminal for communications with said second Home Agent, and a lifetime, said lifetime being of any duration including an infinite duration, of the address used by said at least one mobile terminal for communications with said first Home Agent.
 56. The AAA platform according to claim 51, further configured to establish a security association for protecting communications between said at least one mobile terminal and said second Home Agent, comprising sending to said second Home Agent at least one secret to establish said security association, and deducing said at least one secret from said at least one mobile terminal from an authentication procedure performed by said AAA platform. 